A processor to be used for a portable information terminal is required to consume low power. For this reason, it is considered to replace a cache memory, a main memory, etc. with a non-volatile memory. An MRAM (Magnetoresistive Random Access Memory) attracts attention because the MRAM satisfies all of three feature requirements of high rewrite durability, high-speed read and write performances, and highly integratable cell areas, among a variety of non-volatile memories. There are high expectations to the MRAM because the MRAM has a higher operation speed than other non-volatile memories when the MRAM is used as a cache, the MRAM has higher area efficiency than conventional memories, and a large-capacity high-speed cache can be built in a processor. Especially, among MRAMs, a perpendicular-magnetization spin transfer mode, referred to as an STT-MRAM (Spin Transfer Torque MRAM), is expected for a variety of applications because of an extremely-small read current, an extremely-short write delay, and a high-speed operation.
A DRAM (Dynamic RAMs) conventionally used as the main memory has a large number of memory cells connected on one word line, so that it takes time to drive the word line. Once the word line is driven, access can be made at a high speed to the large number of memory cells connected on the same word line. Therefore, the DRAM is accessible at a high speed to successive address areas. However, when access is made to non-successive address areas, the access speed is drastically lowered because it takes time to drive a word line associated to the non-successive address areas.
On the other hand, in the case of the MRAM, although there is no particular difference in the access speed to both of the successive and non-successive address areas, the access speed to the successive address areas may be lower than that in the case of the DRAM.
As explained above, the DRAM is suited for writing to the successive address areas, whereas the MRAM is suited for writing to the non-successive address areas.